The present invention relates to a plasma processing method and apparatus, such as an etching method and apparatus, to be used for manufacture of semiconductors or other electron equipment and micromachines.
For manufacture of semiconductors or other electron equipment and micromachines, demands for etching techniques related to refractory metal films have been increasing year after year.
For example, in the field of semiconductor memories (storage devices), although countermeasures for increases in the capacitance of memory capacitors have hitherto been given by changing the memory capacitor structure, it has become difficult to secure demanded capacitances only by the structure change with progress of miniaturizing. Due to this, ceramic base oxides having high dielectric constants such as barium/strontium titanate, lead zirconium titanate, and bismuth/strontium tantalate have come to be used as materials for capacitor capacitance. Since elimination of oxygen from these ceramic base oxides would cause their characteristics to largely deteriorate, such materials exhibiting low reaction with oxygen as ruthenium, platinum, iridium, and rhodium are used as materials for capacitor electrodes. Forming microfine patterns by using these materials requires etching techniques for those materials.
Moreover, not only for Si-based semiconductors but also for compound semiconductors, there has arisen a need for an etching process in which contact holes are formed in an insulator film with a refractory metal film used as an undercoat film. In this case, although the insulator film is targeted for the etching, the refractory metal, which is the undercoat film, also would be etched to some extent in overetching.
An etching using an inductively coupled plasma source as an example of the prior-art etching method is explained below with reference to FIG. 7. Referring to FIG. 7, while a vacuum chamber 1 is maintained at a specified internal pressure by exhausting the vacuum chamber 1 with a turbo-molecular pump 3 serving as an exhauster and simultaneously supplying a specified gas from gas supply equipment 2 into the vacuum chamber 1, a high-frequency power of 13.56 MHz is supplied to a coil 6 provided on a dielectric plate 20 by means of a coil-use high-frequency power supply 4, by which plasma is generated in the vacuum chamber 1, allowing the etching on a substrate 8 placed on a substrate electrode 7 to be achieved. Further, a substrate-electrode use high-frequency power supply 9 for supplying a high-frequency power of 400 kHz to the substrate electrode 7 is provided, allowing ion energy reaching the substrate 8 to be controlled.
The turbo-molecular pump 3 and an exhaust port 10 are disposed just under the substrate electrode 7, and a pressure-controlling valve 11 for maintaining the vacuum chamber 1 at the specified pressure is an up-down valve located just under the substrate electrode 7 and just over the turbo-molecular pump 3.
With an etching apparatus having such a constitution, an iridium film can be etched under the conditions of an Ar/Cl2 of 260/20 sccm, a pressure of 0.3 Pa, and an ICP (coil power)/BIAS (substrate-electrode power) of 1500/400 W.
Further, a silicon oxide film on a gold film can be etched under the conditions of an Ar/CHF3 of 270/30 sccm, a pressure of 2.5 Pa, and an ICP/BIAS of 1500/600 W.
However, in the etching of iridium described in the prior art example, which consists mainly of physical etching, an electrically conductive iridium thin film would deposit on the surface of the dielectric plate 20. Therefore, a high-frequency electromagnetic field generated in the vacuum chamber 1 as a result of supplying high-frequency power to the coil 6 would be gradually weakened, and a decline of the etching rate would occur as an issue as shown in FIG. 8.
Also, in the etching of a silicon oxide film described in the prior art example, in which gold forming an undercoat film would be etched to some extent in overetching, where the etching of gold also consists mainly of physical etching, an electrically conductive gold thin film would be deposited on the surface of the dielectric plate 20. Therefore, a high-frequency electromagnetic field generated in the vacuum chamber 1 as a result of supplying high-frequency power to the coil 6 would be gradually weakened, and a decline of the etching rate would occur as an issue as shown in FIG. 9.